As materials of optical lenses, particularly spectacle lenses, plastic base materials have been frequently used instead of inorganic glass base materials in recent years. The reason is that not only the plastic base materials are excellent in properties such as lightweight property, impact resistance, processability and dyeing property but also improvement and development of the materials as plastic lenses of the second generation have been made to promote further lightening and increase of refractive index. These plastic base materials, however, have a disadvantage that they are liable to be scratched as compared with the inorganic glass base materials.
In order to avoid this disadvantage, the surface of an optical lens using the plastic base material is usually provided with a silicon-based coating film, that is, a hard coat layer. In the case of using a plastic lens base material having a high refractive index, metal oxide fine particles are further incorporated into the hard coat layer to adjust the refractive index of the hard coat layer to or near to the refractive index of the plastic lens base material, so as to avoid interference of light (which appears as interference fringes) that occurs between the plastic lens base material and the hard coat layer.
For example, in a patent document 1, it is disclosed to use, as the metal oxide fine particles, composite oxide fine particles containing titanium oxide, zirconium oxide and antimony pentaoxide. Although a hard coat layer formed by the use of a coating composition containing these fine particles is improved in the refractive index of the coating film, it exhibits insufficient adhesion property in the weathering resistance test.
In a patent document 2, also the present inventors have proposed to use, as the metal oxide fine particles, composite oxide fine particles comprising titanium, silicon, and zirconium and/or aluminum. Although a hard coat layer formed by the use of a coating composition containing these fine particles exhibits a high refractive index and is improved also in the adhesion property in the weathering resistance test, there is yet room for further improvement in the adhesion property.
In a patent document 3, the present inventors have proposed to use, as the metal oxide particles, composite oxide fine particles each of which comprises a composite solid solution oxide (i.e. core particle) comprising a composite oxide of titanium and tin with a rutile-type crystal structure and having a surface coated on the core particle with a composite oxide (i.e. coating layer) of silicon and zirconium and/or aluminum. A hard coat layer formed by the use of a coating composition containing these fine particles exhibits a high refractive index and has excellent properties of weathering resistance, light resistance, scratch resistance, impact resistance, adhesion property and the like, but in the case where an antireflection film is formed on a plastic lens base material with the hard coat layer, there is yet room for improvement from the viewpoint of preventing coloration into blue (i.e. bluing) in an atmosphere of exposure to ultraviolet rays.
In a patent document 4, the present inventors have proposed to use metal oxide fine particles each of which comprises a titanium oxide-containing core particle and a coating layer composed of antimony oxide. A hard coat layer formed by the use of a coating composition containing these fine particles exhibits a high refractive index and has excellent properties of weathering resistance, light resistance, scratch resistance, impact resistance, adhesion property and the like, but in the case where an antireflection film is formed on a plastic lens base material with the hard coat layer, there is yet room for improvement from the viewpoint of preventing coloration into yellow (i.e. yellowing) in an atmosphere of exposure to ultraviolet rays.                Patent document 1: Japanese Patent Laid-Open Publication No. 264806/2003        Patent document 2: Japanese Patent No. 3203142        Patent document 3: Japanese Patent Laid-Open Publication No. 204301/2000        Patent document 4: Japanese Patent Laid-Open Publication No 363442/2002        